Satellite communication systems may allow users to access a communications network as the user moves. Some satellite communications systems partition the service area into geographic regions wherein each geographic region is covered by a spot beam which provides communications service to user terminals located within the corresponding geographic region. The user terminal may be a radio telephone capable of communicating with the satellite communication system.
FIG. 1 illustrates a plurality of spot beams 101, 102, 103, and 104 within a satellite communications system which provide service to user terminals located in the corresponding Geographic regions within the service area 100. For example, the satellite communications system provides service to the user terminal 110 located within the corresponding geographic region via spot beam 101. The user terminal may be required to register with the satellite communications system so that service may be provided. Consequently, if the user terminal 110 moves from a first geographic region to a second geographic region within the serviced area, the user terminal 110 may stop acquiring service in the first geographic region and start acquiring the service in the second geographic region to maintain the user's access.
Each of the spot beams may broadcast system information over an associated control channel. The satellite communications system may select a different control channel for each spot beam servicing a portion of the service area. For example, the control channel frequencies and/or time slots may be different so as to reduce interference between spot beams serving proximate geographic regions. The system information may include the location area code for the serving spot beam, a list of control channels used by the satellite system, and any changes in the control channels which may be pending. As will be understood by those of ordinary skill in the art, a channel can be defined by a frequency (FDMA), a frequency and a time slot (TDMA), or other techniques known in the art.
The registration process may require a user terminal to communicate with the satellite communications system. The user terminal may, therefore, receive system information over the control channel associated with the spot beam serving the geographic region in which the user terminal is located. For example, user terminal 110 may register with the satellite communications system by receiving system information on the control channel, determining its corresponding location area code, and updating the satellite communications system with the user terminal's present location area code. The user terminal 110 may be required to re-register with the satellite communications system when the user terminal moves to another geographic region. For example, if the user terminal moves to the geographic region covered by spot beam 103, the user terminal may re-register as being serviced by spot beam 103.
The user terminal may not, however, know the correct control channel for the serving spot beam when the user terminal is powered on or enters satellite mode. Consequently, the user terminal 110 may begin searching for the correct control channel for the spot beam servicing its geographic region. The search may include scanning within a set of known control channels used by the satellite communications system for a signal of appropriate strength. The set of known control channels may be stored in the user terminal 110. For example, if user terminal 110 were powered on in the geographic region covered by spot beam 104, the user terminal 110 may scan the control channels associated with spot beams 101, 102, and 103 before selecting the control channel associated with spot beam 104. Moreover, the process of acquiring the correct control channel may be difficult. For example, in some systems according to the prior art, the user terminal may take several minutes to scan hundreds of control channels before acquiring the correct channel. The search may be required each time the user terminal is powered on in a new geographic region.
Some systems may reduce the search time by having the user input a code which identifies the location of the user terminal. The user terminal may reduce the search time by searching the control channels used in the location. This technique, however, may require the user to carry a list of location codes. Moreover, the user may be required to input the location code in a particular format which the user may not know. The user may also make an error in entering the location code. In consideration of the above discussion, there is a continued need to reduce the time for a user terminal to register with a satellite communication system.